f(x) = a.x . We ha to calculate a.
Back to the table, let's rewrite the coordinates
A(0,0)
B(2,-1)
C(4,-2)
D(7,-3.5)
We know that constant is called slope or coefficient is equal to:
a=y/x
Apart from A, in each of the coordinates y/x =-1/2 & this is the slope of the equation f(x) = (-1/2)x